1. Field of the Invention
The present invention relates to a circuit board with a conductor circuit formed on an insulating layer, a covering formed on the conductor circuit and a terminal connected to the conductor circuit penetrating through the covering.
2. Description of the Related Art
In recent years, with development of high speed and sophistication of electronic appliances, micromachining of several shapes is required on a circuit board on which an electronic component such as a semiconductor element or magnetic head is mounted. It is not too much to say that the reliability of the electronic appliance depends on the machining accuracy.
Generally, a terminal for connecting an electronic component is installed on the circuit board. The terminal surface is made of copper (Cu), nickel (Ni), gold (Au), etc. The terminal on a conventional circuit board was manufactured in such a manner that the surface of the conductor circuit is subjected to a prescribed electrolytic metal plating and a covering having a through-hole is formed on the surface. Specifically, the terminal portion, as shown in FIG. 4, has a structure in which the metal-plating surface exposed from a through-hole 33 of the covering 3 constitutes a terminal surface. In FIG. 4, the surface of the terminal 8 is made of an electrolytic-plating Au thin film 7.
The terminal of an electronic component mounted on such a circuit board and that of the circuit board are generally connected to each other through a metallic ball.
However, at the terminal portion of a conventional circuit board as shown in FIG. 4, generally, there is a level difference 30 of 4 .mu.m or more between the covering surface and the terminal surface (surface of the conductor circuit). The level difference corresponds to thickness of the covering. As shown in FIG. 5, presence of such a level difference may lead to poor connection between the terminal 32 of the electronic component 31 and the terminal 8 of the circuit board by the metallic ball 34. Namely, in FIG. 5, the metallic ball 34 is brought into contact with the terminal 8 of the circuit plate but not with the terminal 32 of the electronic component.